JP 4252091B discloses a power supply control apparatus that controls power supply to a load from a DC power supply, which is typically a battery. In this power supply control apparatus, a semiconductor switch is arranged midway in a power supply path through which the DC power supply supplies power to the load. A current flows through the power supply path if the semiconductor switch is ON, and no current flows through the power supply path if the semiconductor switch is OFF. Power supply from the DC power supply to the load is controlled by switching ON and OFF the semiconductor switch.
In the power supply control apparatus described in JP 4252091B, the DC power supply is connected to a control end of the semiconductor switch via a switch. When the semiconductor switch is switched from OFF to ON, the switch is switched from OFF to ON. Thus, electric power is supplied from the DC power supply to a parasitic capacitor with an end connected to the control end.
The voltage at the control end increases with an increase in electric power stored in the parasitic capacitor. If the voltage at the control end becomes greater than or equal to an ON threshold, the semiconductor switch switches from OFF to ON. The DC power supply can continue to supply a large amount of electric power to the parasitic capacitor for a long period of time. Thus, in the power supply control apparatus described in JP 4252091B, the semiconductor switch can be quickly switched from OFF to ON.